Vehicles powered by internal combustion engines may be cooled by a coolant circulating in jackets surrounding combustion cylinders. The coolant may be heated by the engine and is then cooled for recirculation by a heat exchanger. The heat exchanger may be cooled by air with air flow enhanced by a fan. The fan may be driven by an engine crankshaft, may be electrically driven by the vehicle electric system, or may be driven by a hydraulic system.
Some known methods for controlling a fan speed use a coolant temperature signal for regulating, for example, a fan speed or blade pitch. Such a method my increase the fan speed or the blade pitch, as the coolant temperature increases. For example, when a vehicle experiences a high load, the heat dissipation increases, driving the coolant temperature higher. When this happens, the fan speed or blade pitch is increased to improve air flow and to deal with the higher heat dissipation required in the cooling package. This results in higher fan power needs, which must be provided by the engine. Because the engine is already at, or near, peak load from the work function of the vehicle, the added fan drive power may cause the engine to be overloaded, and the operator may need to slow down or otherwise reduce the vehicle load. At high loads, this reduces productivity and fuel efficiency.